The present invention relates to a novel synthetic route for the production of 1-aminoanthraquinones.
1-Aminoanthraquinone is a well known and important intermediate used in the preparation of colorants including dyes and pigments as well as other specialty chemicals. 1-Aminoanthraquinone is particularly useful as an intermediate in the preparation of fiber-reactive dyes. Thus, in the past, most dyes were dispersed dyes which relied on surface properties such as static interaction to bond to a fabric. Presently, new fiber-reactive dyes which react with chemical sites on the fabric fibers have provided a significant improvement in the ability of the dye to remain bonded to the fabric. 1-Aminoanthraquinone is an intermediate for the formation of such fiber-reactive dyes. For example, 1-amino-4-bromoanthraquinone-2-sulfonic acid (Bromamine Acid), an important intermediate in a fiber reactive dye, can be formed by treatment of 1-aminoanthraquinone with oleum or chlorosulfonic acid to form the 1-aminoanthraquinone-2-sulfonic acid derivative which is then followed by treatment with bromine. This brominated compound can be subsequently reacted with another compound which can couple with the fabric fiber. Importantly, the chromophore, i.e., the 1-aminoanthraquinone, becomes part of the molecule which couples with the fabric fiber. It is important that the amino group be located on the 1 position of the anthraquinone inasmuch as the placement of the amino group on other positions of the anthraquinone yields a color body of a different color.
1-Aminoanthraquinone has been prepared by the reaction of anthraquinone with oleum in the presence of mercury to produce anthraquinone-1-sulfonic acid which, in turn, is reacted with ammonia. However, mercury is a known toxic chemical and thus, poses severe environmental problems with its use. In an alternative process to produce 1-aminoanthraquinone, anthraquinone is nitrated directly followed by reduction of the nitroanthraquinone. Unfortunately, direct nitration of anthraquinone yields a mixture of products including 1-, 2-, and dinitroanthraquinones which upon hydrogenation yield the corresponding aminoanthraquinone mixture. Consequently, the product which is formed subsequent to reduction yields more than one color body and intricate methods of separation must be used to obtain the pure 1-aminoanthraquinone. Not only with nitration, but with other processes which attempt to add a functional group which can be converted to an amino group, selectivity to the 1-position is marginal as other isomers are formed or complicated process schemes are required to fix the amino group at the 1-position on the anthraquinone.
Accordingly, it is an object of the present invention to provide a commercially feasible and economical process for the selective production of 1-aminoanthraquinone and substituted derivatives thereof without the disadvantages of the prior art processes as mentioned above.